See examples of Fungi Rot: example 1, example 2, example 3, example 4

An Understanding of WOOD DESTROYING FUNGI

A basic definition of Fungus is "a plant which does not contain Chlorophyll." Fungus may be found virtually everywhere in nature where sufficient moisture exists for their survival. There are two major groups of Fungi that may occur on wood: Stain Fungi and Decay Fungi.


Stain Fungi usually is visible as a discoloration of the wood. Although the Stain Fungi are feeding on the wood in their active stage, they do so at an extremely slow rate.

Decay Fungi is of major importance as a destroyer of the strength of wood. Within this group of Decay Fungi there are two kinds which are of concern. These are White Rot and Brown Rot.

White Rot attacks only hardwood and works slowly, feeding on both the cellulose which composes the cell as well as the liginin, (the "glue" in wood). The results of the attack by the fungi is a resulting white, spongy appearance in the wood.

Brown Rot attacks only softwoods, feeding only on the cellulose, and working very quickly. In Ideal conditions for growth, "decay" could begin in as little as 3 to 4 months, from initially sound lumber. Softwoods such as Pine or Fir are those used most often in the vast majority of structural framing.

Two species of Brown Rot are of importance in the integrity of the wood structures. Merulius Lacrymans, also called "tear drop fungus," gets its name from water droplets that may form on its fruiting body know as sporphore. The most common wood destroying fungus and the most important throughout the US is Poria Incrassata. It is a serious problem only on the softwoods.

Environmental Requirements of Fungi:
Most organisms require four basic conditions in order to survive and multiply. These conditions are food, water, oxygen and the proper temperature range. Extremes of temperature may put fungi into a dormant state, usually known as spores, but may not kill them completely.

Food for the fungus is the wood that homes are built from. Barriers such as paint, varnishes help in maintaining to control fungus, but these barriers cannot completely provide protection.

The ideal temperature favoring quick growth of Poria is about 72" - 74" fahrenheit. As the temperature lowers the growth of Poria slows, and may halt altogether, but the Fungus has not died. It may be able to resume growth when the temperature returns to a more optimum range. The spores, or "seeds"of fungus are usually very hardy and can survive some extremes in their environment for long periods of time.

The most important of the four conditions needed by fungus is moisture. Living wood may have up to 90% (by weight) water in and around its cells. kiln-drying of wood may decease the moisture to as low as 8%.

Wood with a moisture content below 20% will not support the growth of fungus, and at 8% moisture the fungus will be killed. However, Poria requires actual visible standing water in order to begin growth. Fungus growth cannot start until water droplets are formed outside the cells.

The speed with which a Poria colony can destroy wood varies greatly, depending on the various factors. However, some approximate values have been established to the loss of various strengths in wood at between 5 - 10% loss in weigh, all being due to fungus feeding.

At 5-10% loss of weight:
- Toughnessdown by 80 %
- Impact resistancedown by 80%
- Compression strengthdown by 60 %
- Shear strength & hardnessdown by 20%